Blue whiting in Icelandic waters: migration, residency, and population connectivity

Abstract

Widely distributed pelagic fish populations underpin some of the largest fisheries globally and play a critical role in ecosystem dynamics by driving nutrient cycling and carbon transfer through vertical and seasonal migrations. Effective fisheries management requires understanding their spatial distribution, abundance, size structure, and the environmental factors that drive temporal variations, especially in the context of climate change. Here, we investigate the population structure of blue whiting (Micromesistius poutassou) in Icelandic waters using Bayesian hierarchical spatiotemporal models applied to bi-annual demersal survey data (1996–2023), which included 15,788 samples. Our results show that blue whiting occurrence, abundance, and size structure are influenced by physical (depth, bathymetric slope), environmental (SST, SBT), and temporal (time of day, year, season) factors. We identify three main spatial patterns: persistent aggregations along the southern shelf and Iceland-Faroes Ridge, intensifying in spring; (2) marginal transition zones to the northwest and northeast with spatiotemporal variability; and (3) fringe subpopulations in the north. These findings suggest that migration from the dominant Northeast Atlantic population primarily drives autumn distributions, while partially resident juveniles persist in local nursery areas on the southern and western shelf year-round. This study provides vital knowledge for sustainable management on blue whiting stock level responses to future climate change.